On the one hand, it's very difficult to speak about specifics regarding depression without first-hand knowledge of a particular situation. However, we are indeed commanded to rejoice always (Phil 4:4; 1Th 5:16). To the degree that anyone doesn't do that, they've sinned. There is simply no way to argue with that.
And yet, what about cases of depression that we hear are set off by physical factors, such as a vitamin deficiency, or extremely traumatic factors, like a cancer diagnosis, a botched surgery, or terrible childhood memories? Immediately our instincts of compassion want to explain how the person can't be at fault for such things so out of their control.
Treating the Spiritual as Physical
However, to be frank, there is just a world of subjectivity and assumption in the assertion that a particular case of depression was caused by any one or combination of things. For one thing, it's scientifically impossible to declare with confidence that the depression was "set off" by anything physical. The science in determining the the relationships between cause and effect, and between physiological and psychological, regarding depression is extremely murky. Physiological symptoms which are supposed to be the cause of psychological symptoms may in fact be the effect of a troubling problem in one's life. There is actually no conclusive research that proves we can tell which way the causal arrow points. Therefore, saying that depression may be set off, or caused, by something like a vitamin deficiency or chemical imbalance is more of a theory than a reality.
Following the above thinking, many people speak of depression as a diagnosis. But really that is a misnomer. Depression describes a state of the mind or of the soul. After all, that is what the term psychology means: the study of the soul. It's the same way that mental illness is a misnomer. Illness describes a physical, physiological infirmity that is treated with a physical or physiological treatment. The mind, by definition, cannot be ill. And again, though there are certainly physical issues regarding depression, there's no conclusive evidence that has proven that any particular physical impairment caused the psychological impairment. It can just as well be an effect as the cause.
But even if we were to grant that physiological conditions did indeed cause a particular case of depression -- which, again, we can't possibly know; and please hear the gentleness in what may seem to be a firm statement -- it would still be the person's responsibility before God to respond to those very unpleasant circumstances righteously. Not doing so is sinful.
How Depression Develops
Let me illustrate with an example, which is my own but is adapted from Jay Adams' Christian Counselor's Manual, pp. 375ff:
Depression develops as the result of a downward spiral of unbiblical responses to circumstances of life. First, there is an original problem which may or may not be the person's fault. For example, a man finds out he has prostate cancer – something largely, if not entirely, out of his control. Yet, rather than receive the cancer as a trial from God (Rom 8:28; Jas 1:2-4; 1Pet 4:12-13), and as an opportunity to make much of God in his response by resting in His sovereign goodness, he becomes worried and self-focused. Then, rather confronting his worry Biblically (cf. Mt 6:25-34; 1Pet 5:7), this worry slowly produces complicating problems such as a fatalistic attitude as he begins neglecting responsibilities. His neglect of responsibilities elicits more unbiblical responses until all his multiple problems plunge him into depression. Adams summarizes, "The downward cycle of sin moves from a problem to a faulty, sinful response, thereby causing an additional complicating problem which is met by an additional sinful response, etc." (CCM, p. 375). It is important to note that depression is the result of the sinful responses to the initial problem of a cancer diagnosis, and not the cancer diagnosis itself.
The Myth of "No Control"
Many people (1) seek absolution for themselves or (2) seek to offer comfort to others by asserting that the depressed person has no control over his depression. However, as mentioned before, he may have had no control over the initial problem, but -- and again, please don't hear unfeeling harshness, but tenderness, even in a firm statement -- as someone responsible before God, he does have control over how he responds to that initial problem.
Those who hasten to declare that depression is something over which we have no control do so because they don't want someone who is struggling with depression to heap more blame on themselves, and thereby increase their depression. That is, the fear is that if a depressed person believes that his depression his fault and that he is responsible to feel differently, he will just feel greater pressure and feel worse about himself for not having been able to do anything about it.
We've got to recognize, though, that if a person confronted with that reality responded in that way, it would be a sinful response. Such a response comes from a self-focus, and trusting more in circumstances and others' evaluations of them than in the grace of Christ. And remember, the culprit of compounding depression is sinful responses to unpleasant or unwanted circumstances. So if someone were to respond that way, it would quite possibly further his depression.
But I don't think the alternative is to tell him he has no control over it. In fact, I'd be concerned if depressed people believed that they have no control over their depression, that it's not necessarily sinful (so not their fault), and so that any hope of recovering is out of their control. Insisting that depression is a result of sinful responses means that at any point (by the grace of God in Christ and the work of the Holy Spirit) a child of God can respond righteously, and can reverse that downward spiral of increasing depression. After all, "if you do well, will not your countenance be lifted up?" (Gen 4:7). Perhaps bringing up a depressed person's responsibility may be painful and bring sorrow at first, but I would hope that it would be a godly sorrow which leads to repentance (2Cor 7:8-10). If they can learn that they must confess and repent of their joylessness, that to me would seem to be wonderful progress!
So, insisting that depression is a result of sinful responses gives more hope than does insisting that they have no control over it.
I hope I've treated this matter clearly, but also sensitively. I don't mean to be insensitive to real, hurtful problems. To those experiencing the pain that goes along with these kinds of things, I hurt along with you (1Cor 12:26). Yet because the believer's joy in God-in-Christ is at the heart of glorifying God as He's worthy, and because that is what my entire life is supposed to be about, I believe it is so important to order our thinking aright in this matter, even if it means saying and taking a stand on some hard things. After all, the best defense against unbiblical thinking during trials is a strong offense of Biblical thinking prepared in advance. I hope these thoughts are received in the spirit in which they were intended.
"Can a woman forget her nursing child, and have no compassion on the son of her womb?
Even these may forget, but I will not forget you.
Behold, I have inscribed you on the palms of My hands."
- Isaiah 49:14-16 -